1. Field of the Invention
The present invention relates to an element substrate for a detachable printhead having a connection status output circuit that outputs a signal in response to an electrical connection status of a printhead and a printing apparatus. Furthermore, it relates to a printhead, a head cartridge, a printing apparatus, and methods for confirming an electrical connection status of a printhead and a printing apparatus.
2. Description of the Related Art
Techniques that use an electromechanical transducer such as a piezoelectric element and techniques in which ink is heated using an electrothermal transducer (heater) to discharge an ink droplet using a film boiling effect are known as typical ink discharge techniques of printheads that are mounted in an inkjet printing apparatus.
A printing apparatus provided with the aforementioned inkjet printhead is capable of outputting high quality text and images at low cost. In particular, a printer in which ink droplets are discharged using a film boiling effect have an advantage in being capable of carrying out color printing at low cost and therefore hold a major share of the market.
Due to a tendency to improve image quality, the number of discharge orifices of a printhead has generally increased from 64 to 128 outlets, or even 256 outlets or the like, which are arranged in a high density manner having a number of discharge orifices per inch (dpi) of 300 dpi or 600 dpi for example. The heaters arranged as electrothermal transducers for the respective discharge orifices form respective bubbles due to film boiling with heat pulses of a several microsecond order to a 10 microsecond order. By driving at high frequencies in this manner, high image quality prints can be achieved at high speed.
Means for electrically connecting the printhead in the inkjet printing apparatus is provided in a carriage in which the printhead is mounted and conveyed reciprocally. Specifically, a plurality of contact points are provided in the carriage which are made to respectively contact a plurality of contact points provided on the printhead when the printhead is mounted in the carriage. In this manner, electrical connection is achieved between the printhead and the inkjet printing apparatus.
Exchangeable printheads are commonly designed to be replaced by a user, and in an inkjet printing apparatus that uses the printhead integrated with an ink tank, a new printhead is mounted each time the ink is exhausted. An electrical connection between the printhead and the inkjet printing apparatus is established each time a printhead is replaced with a new printhead by a user, and therefore it is preferable to monitor the electrical connection status between the printing apparatus and the printhead. U.S. Pat. No. 5,828,386 discloses a printhead and an inkjet printing apparatus that are provided with means for monitoring the electrical connection status. This relates to a print signal that is supplied from the printing apparatus to an input terminal of the printhead, a clock signal for transferring the print signal, and a control signal for enabling a printing operation in response to the print signal. U.S. Pat. No. 5,828,386 involves a configuration provided with an AND circuit that performs computation on a logical product of these three signals, and an output terminal for outputting a result of the computation.
FIG. 3 is one example of a conventional connection status output circuit. Here, there are a print signal (DATA), a clock signal (CLK), a drive signal (HE) for driving a heater, and a latch signal (LT) for latching the print signal in a latch circuit (not shown). The logical product of these signals undergoes computation in the AND circuit, and a computation result is outputted by a connection status output terminal (CNO). A CNO signal is high only when the latch signal, the drive signal, the print signal, and the clock signal are all high. Accordingly, the electrical connection between the printhead and the printing apparatus is confirmed when all the input signals are inputted at high level at a certain arbitrary timing from the printing apparatus and the CNO signal is outputted at high level. In this manner, it is possible to confirm whether or not the printhead is connected properly to the printing apparatus, and therefore it is possible to prevent printing problems such as missing print dots, and damage to the printhead originating in contact point problems.
Furthermore, U.S. Publication No. 2007/0002087 discloses a circuit and a terminal that output a connection status of a CLK signal, a DATA signal, an LT signal, and an HE signal.
In this regard, a printhead designed to be capable of being replaced by the user will be touched directly by the user at times such as during replacement. For this reason, for example when static electricity is produced when the printhead is touched directly by the user, an electric current of that static electricity will be supplied to the element substrate via the terminals of the printhead and the wiring, and portions of the element substrate susceptible to the static electricity may be damaged. Thus, it is necessary to adopt a technique such that damage is not inflicted on the element substrate.
A configuration in which an electrostatic protection element constituted by a diode is inserted between the input portion of the print signal and the power line and ground line respectively are commonly implemented as resolving means. In this way, the electric current that flows in as static electricity is distributed and flows out to the power line and the ground line, thereby improving the robustness of the element substrate against static electricity.
However, a printhead that can enable confirmation of its electrical connection status and in which an electrostatic protection element is provided has problems such as the following. When signals being high level are inputted from signal terminals during a confirmation of the electrical connection, an electric current may flow undesirably to the power line through the electrostatic protection element. When the electric current flows undesirably to a logic power source (VDD) that is a power line, the connection of the VDD terminal alone may not be able to be confirmed. FIG. 2 shows a configuration example of an electrostatic protection circuit in which diodes are used as an electrostatic protection element. The diodes, which are an electrostatic protection element, are provided near a print signal input pad at the VDD line side and the ground side, respectively. With this configuration, the electric current that flows in as static electricity is distributed externally and flows out. Here, a voltage of 3.3 V, for example, is applied to each print signal terminal when confirming the electrical connection status. However, even if the VDD terminal has a connection problem, a voltage of approximately 2.6 V is supplied through the diode to the VDD line, and therefore this voltage is confirmed as a VDD voltage when confirming the electrical connection status. There is no problem if connection to the VDD terminal is established and electricity flows. However, if a heater driving voltage VH (for example, 24 V) is applied while the VDD terminal has a connection problem, there is a risk that the printhead will be damaged due to malfunction of the heater caused by an operation of the logic circuit being indefinite. Accordingly, in a printhead having both an electrical connection output circuit and an electrostatic protection circuit, it is preferable that this is configured to enable the electrical connection status of the logic power source to be confirmed independently in order to provide greater reliability. Although U.S. Publication No. 2007/0002087 discloses a circuit and a terminal that output a connection status of the CLK signal, the DATA signal, the LT signal, and the HE signal, it is not a configuration that enables the electrical connection status of the logic power source to be confirmed independently.